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Configurations

Why do elements react?

An ion is an atom or molecule with a net
electric charge due to the loss or gain of one
or more electrons
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They must be stored
under oil to keep air and water
away from them
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Reactivity of halogens

Positive and Negative Ions: Cations and
Anions
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The non-metal elements in Group
7 - known as the halogens - get
less reactive as you go down the
group
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Fluorine is the most reactive element of all in Group 7
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Explaining trends

Reactions of metals and acids

Testing gases

metal + oxygen → metal oxide

In a reaction, an atom of a Group 1 element will form an ion with a single positive charge
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They are placed in the vertical column on the
left-hand side of the periodic table
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Group 7 elements form
salts when they react with metals
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Ions and ionic compounds

Group 1 – the alkali metals

The Group 7 elements are called the halogens
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Elements to react to complete their outer
shell; they lose or gain an electron(s)
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Group 7 – the halogens

salt + carbon

metal + water → metal hydroxide + hydrogen
Displacement reactions
If a reactive element comes into contact with the compound
of a less reactive element a chemical reaction may take place
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chlorine + sodium bromide →
sodium chloride + bromine
chlorine + sodium iodide →
sodium chloride + iodine
bromine + sodium chloride →
no reaction

Covalent bonds
A covalent bond forms when two non-metal atoms share
a pair of electrons
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An atom that shares one or
more of its electrons will complete its outer shell
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Substances with covalent bonds often form
molecules with low melting and boiling points, such as
hydrogen and water
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The ions formed have a stable electronic structure, like a noble gas from Group 0
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The Pauling
scale is the most commonly
used
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0, and
values range down to
caesium and francium which
are the least electronegative
at 0
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There are more than 100 different elements
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The vertical columns in the periodic
table are called groups
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The periodic table has eight main groups
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There are no compounds in the periodic table, because these consist of two or more different
elements joined together by chemical bonds
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A hydrogen atom with one electron
and a chlorine atom with 17 electrons

2
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The protons and neutrons are
found in the nucleus at the
centre of the atom
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The electrons are
arranged in shells around the nucleus

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